1. Field of the Invention
The present invention relates to an apparatus used in the manufacturing of integrated circuits (ICs) and, more particularly, to a bake unit for heating or cooling substrates.
2. Description of Related Art
As the integration density of semiconductor devices has increased in recent years, unit areas of cells become smaller and circuit linewidths become finer. Therefore, photolithography is increasingly becoming significant.
Photolithography includes deposit, expose, develop, and bake processes. The bake process is a process for heating or cooling substrates at a determined temperature, which is performed before or after each of these processes is performed. The bake process includes a heating step in which substrates are heated by means of a heating plate and a cooling step in which substrates are cooled by means of a cooling plate. Generally, the cooling step is followed by the heating step.
A bake apparatus for performing a cooling step includes a cooling plate to cool substrates. A substrate is loaded on the cooling plate by means of a lift pin. When the substrate is cooled on the cooling plate, it faces convexly upward. When a substrate heated by means of a heat plate is loaded on the cooling plate, a temperature of air in a space between the cooling plate and the substrate is high. As a cooling step is performed, the temperature of the air drops. Thus, the air is compressed and an inner pressure of the space becomes vacuum or lower than an outer pressure thereof. When the lift pin lifts up the substrate after the cooling step is completed, a strong force is applied to the substrate to damage the substrate.
Further, if the lift pin descends when a substrate is loaded on the cooling plate (or heating plate), air remaining in the space between the substrate and the cooling plate (or heating plate) flows to the exterior of the space. However, if the substrate approaches the cooling plate (or heating plate), a flow path of the air remaining in the space becomes narrower to lower a flow rate of the air exhausted to the exterior of the space. For this reason, the substrate may be located out of position due to the air pressure in the space. Such a problem becomes severe with the recent trend toward larger substrate diameter. Although this problem may be solved by reducing a descending speed of the lift pin, there arises another problem that a process time increases.